1. Field of the Invention
The present invention relates to a method of monitoring discharge of liquid, and more particularly to a method of detecting whether the discharge operation has been reliably carried out during the discharge of liquid from a vessel. The present invention also relates to an apparatus for practicing the method of monitoring the discharge of liquid .
2. Description of the Related Art
For example, in a biochemical analysis of which an immunoassay such as a heterogeneous immunoassay is representative, first, a sample, for example, a serum to be assayed, is injected into a reaction vessel which contains a solid phase carrying an antibody required for an immune reaction, a label antibody and the like to induce the immune reaction with an antigen in the sample, so that an immune reaction complex is formed on the solid phase. Subsequently, a washing operation referred to as a B(Bind)/F(Free) washing is carried out to remove a label antibody which does not contribute to the formation of the immune reaction complex, and finally the remaining label quantity is measured.
The washing operation referred to as the B/F washing includes the operation for discharging the liquid out of the vessel, and the operation for injecting a suitable washing solution, a reagent solution or the like into the vessel. The discharge operation is performed, for example, using a liquid discharge apparatus comprising a tube adapted to serve as a liquid discharge outlet and a passage as well, an end of which tube being connected directly or indirectly to a liquid suction force generator such as a negative pressure generator, in such a way that the end of the tube is penetrated into the liquid in the vessel. Consequently, it is usual for an automatic immunoassay apparatus or the like to equip a washing solution supply device and a liquid discharge apparatus between a sample/reagent injection apparatus and the measuring apparatus.
Also in a general chemical analysis, for example, in a case where the same reaction vessel is repeatedly used, the used vessel will be washed every use. This washing operation includes both the operation for injecting a washing solution into the vessel, and the operation for discharging a washing solution out of the vessel. It is usual for such an assay apparatus to equip a washing solution supply device and a liquid discharge apparatus after the measuring apparatus.
There is a need to provide the operation of exhausting a reaction solution from the reaction vessel, sometimes, for example, also in a case where the reaction solution is introduced from the reaction vessel to a flow cell for a measurement, other than the discharge operation for a liquid such as a washing solution as mentioned above.
For example, in the B/F washing in the automatic immunoassay apparatus, an incompleted discharge of liquid from a reaction vessel has a significant effect on the measurement result and also brings a danger such that the liquid in the reaction vessel overflows when a washing solution is injected into the reaction vessel. The overflow hinders the mechanical movement, corrodes the structure and causes the current leakage. Further, there is such a possibility that a biosample such as a blood serum as a sample contains the virus having an infectivity. Thus, the overflow of the liquid out of the vessel must be avoided as much as possible.
Further, for example, in the washing of a reaction vessel in the automatic chemical analysis apparatus, an incompleted discharge of liquid from the reaction vessel leaves the vessel as stained by the liquid and sometimes the vessel containing a residual washing solution is used for the next measurement. These would have a significant effect on the analysis result.
The following cases may be considered as a cause of an incompleted discharge of liquid from the reaction vessel. That is, as a first case, it is assumed that a tube, which constitutes a passage for a liquid flow of a liquid discharge apparatus, is bent or pinched and thus the passage is closed. As a second case, it is assumed that a suction force of a liquid suction force generator for leading the liquid from the reaction vessel to the discharge pass is weakened owing to an occurrence of any problems on the liquid suction force generator, so that the liquid is not led to the passage. And as third case, it is assumed that there occurs a clogging on an opening formed at one end of a liquid passage or a tube constituting the liquid passage, to be inserted into the liquid so that the passage has been substantially closed.
In order to keep the discharge operation for liquid in good order, according to the prior art, inspection of the liquid discharge apparatus is carried out regularly to keep it in a reliable state, and also even if it is in a good condition, parts used for a given period of time or a given number of times are replaced by new parts. Thus, these measures cope with unexpected situations. However, these countermeasures are not effective to prevent the clogging of the passage or the like which will happen suddenly. Hence, it is requested to provide a method of monitoring as to whether the discharge operation has been reliably performed during the discharge of liquid.